1. Field of the Invention
The present invention relates to a manufacturing method of an evacuated hermetically sealed container, and in particular, to a manufacturing method of an internally vacuumized image display apparatus including an electron emitting device and a phosphor film.
2. Description of the Related Art
Image display apparatuses of a flat panel type such as organic LED displays (OLEDs), field emission displays (FEDs), and plasma display panels (PDPs) are well known. These image display apparatuses include an envelope manufactured by hermetically joining opposite glass substrates together and including an internal space partitioned off from an external space. Such a hermetically sealed container is manufactured by arranging a frame member, and as required, a distance defining member or a local adhesive, between the opposite glass substrates, arranging a joining member in a peripheral portion of the resultant structure in frame form, and heating and thermally joining the frame member and the glass substrate together. Known methods for heating the joining member include baking of the whole glass substrate using a heating furnace and selective heating of the periphery of the joining member by means of local heating. The local heating may be more advantageous than the overall heating in terms of heating and cooling time, the quantity of heat required for heating, productivity, prevention of thermal deformation of the container, prevention of thermal degradation of a functional device arranged inside the container, and the like. In particular, laser light is known as a local heating unit.
U.S. Patent Application No. 2008/0110561 discloses an example in which local heating with laser light is applied to a manufacturing method of an envelope for an OLED. An envelope is manufactured by heating and thermally melting a frit arranged between glass substrates, using laser light. A light shielding mask is formed in a part of each of the glass substrates through which laser light is transmitted. The glass substrates are joined together so that the quantity of irradiated laser light is distributed in a particular manner. The distributed quantity of irradiated laser light effectively serves to maintain the frit at an appropriate temperature. Thus, the frit and the glass substrate can be evenly joined together.
U.S. Patent Application No. 2006/0082298 discloses an example in which local heating with laser light is applied to a manufacturing method of an envelope for an OLED. An envelope is manufactured by heating and thermally melting a frit arranged between glass substrates, using laser light. The scanning speed, power, and heat quantity distribution of laser light are dynamically varied so as to uniformly heat the frit. Hence, the frit is kept at a substantially constant temperature, preventing the glass from being broken.
Japanese Patent Application Laid-Open No. 2009-196859 discloses a method of manufacturing a glass weld by heating and thermally melting, using laser light, a frit arranged between glass substrates to hermetically join the glass substrates together. Bubbled gas can be prevented from entering the inside of the weld by selectively melting only a part of the frit positioned outside the weld.
As described above, the joining method based on the overall heating and the joining method based on the local heating are conventionally known. For the joining method based on the local heating, a joining method is known which involves various irradiation methods improved in the respective manners instead of simple irradiation of the joining member with laser light. However, in the conventional art, when an attempt is made to obtain a heat quantity required to thermally melt and soften the joining member in order to achieve a sufficient joint strength, the joint strength and airtightness of the hermetically sealed container with a reduced pressure may decrease; the container includes the pair of glass substrates and the frame member. Specifically, when the inside of the hermetically sealed container is reduced in pressure, the following occurs because the frame member and the solidified joining member are only slightly compressively deformed: the glass substrates are deformed so as to be recessed inward at a central portion thereof so that the frame member serves as a fixed point. However, the following occurs because the frame member and the solidified joining member cannot follow this deformation: near the boundary between a part of the glass substrates which is in contact with the frame member and a part of the glass substrates which is not in contact with the frame member, the glass substrates are bound by the frame member and subjected to a high tensile stress. As a result, the glass substrate or the joining member may be destroyed, thus reducing the strength reliability and airtightness of the evacuated hermetically sealed container.
An object of the present invention is to provide a manufacturing method of a reliable evacuated hermetically sealed container which container offers both appropriate joint strength and airtightness.